Sensors are used in internal combustion engines to detect various engine operating conditions, such as cylinder pressure. These sensors are typically mounted in a mounting bore formed in a portion of the engine adjacent the engine environment to be sensed by the sensor.
For example, as shown in U.S. Pat. No. 3,371,525 to Mitchell, a cylinder pressure sensor is mounted in a mounting bore formed in a cylinder head of an engine adjacent an engine cylinder. The pressure sensor includes a cylindrical shaped tubular body positioned in a cylindrical mounting bore sized larger than the sensor body to form an annular gap surrounding the tubular body. The inner end of the tubular body includes threads for engaging the cylinder head inside the mounting bore to secure the sensor in the bore. A sealing nut with a beveled edge is provided on the outer end of the sensor body for engaging an O-ring to prevent contaminants from entering the mounting bore. The sensor and mounting bore are necessarily positioned in close proximity to hot combustion and exhaust gases. As a result, after extended operation, removal of the sensor can be difficult due to oxidation and corrosion in the narrow annulus surrounding the sensor. The corrosion and build-up of residue fills the annulus thus binding the sensor to the inner wall of the mounting bore. The sensor is removed by rotating the sensor so that the sensor unscrews from the threads in the bore and moves outwardly out of the bore. Other sensors use a mounting nut positioned on the outer end of the sensor for relative rotational movement so as to engage and disengage threads formed on the outer end of the mounting bore. In both designs, the bond between the sensor and mounting bore created by the corrosion and residue will be broken or loosened by the rotation of the sensor or nut. However, as the sensor is then pulled from the mounting bore, the corrosion residue continues to obstruct the removal of the sensor making removal difficult and time consuming. Also, the O-ring may be damaged during engine operation by excessive gas pressure in the annular gap. The excessive gas pressure develops as a result of an increase in the temperature of the gas in the annular gap surrounding the sensor body during engine operation and/or leakage of combustion gas through the threaded connection at the inner end of the sensor. The excessive pressure moves the seal from its seat disrupting the sealing ability of the seal thereby disadvantageously permitting contaminants to enter the mounting bore and damage and corrode the sensor.
U.S. Pat. No. 4,633,842 to Ikeda et al. discloses a sensor for an engine which includes a sensor body having a two cylindrical portions of respective constant diameters integrally connected by a beveled surface. The cylindrical portions of the sensor appear to be mounted in abutment with the inner annular walls forming the mounting bore. As a result, the high temperature corrosion and residue will likely bond the sensor to the bore wall thereby requiring burdensome and time consuming removal procedures.
U.S. Pat. No. 4,414,531 to Novak is noted for disclosing an oxygen sensor having a cone shaped insulator body positioned in a conical shaped bore of a mounting body. However, the insulator body and the mounting body appear to be connected by a bonding substance and, therefore, no clearance appears to exist between the sensor and body. Thus, this sensor is permanently connected and can not be easily removed from the bore.
U.S. Pat. No. 4,995,256 to Norlien et al. discloses a zirconia cell oxygen sensor having a conical probe positioned in a cylindrical, i.e. non-tapered, cavity. However, the sensor is not used to measure combustion gas of an engine and therefore, the cavity is not exposed to corrosive residue. Since the sensor body is conical and the cavity is cylindrical, the clearance between the sensor and bore does not increase as the sensor is pulled out.
German Patent No. 831166 to Saul discloses what appears to be a spark plug having an inner body having a tapered or conical inner body portion inserted into a tapered receiving bore formed in an outer body. A threaded nut, surrounding the inner body, includes an angled annular wall for compressing a seal. However, Saul no where suggests a sensor for sensing engine cylinder pressure and the disclosed spark plug tip does not include a seal. As a result, an annular gap between the inner and outer bodies is in continuous communication with the engine cylinder. Saul does not disclose a manner for venting the annular gap. In fact, the annular wall and opposing seal seat are positioned to compress the seal so as to apparently prevent sufficient flexing of the seal to allow venting. Moreover, the taper, or angle, of the conical portion is extremely large thereby disadvantageously creating a wide body incapable of conforming to the packaging constraints in the cylinder head of various engines.
Consequently, there is a need for an improved sensor assembly capable of permitting easy removal of the sensor from a mounting bore while preventing contaminants from entering the mounting bore throughout engine operation.